Polyimide films, resin compositions, metal-clad laminates, and flexible circuit boards

Abstract

To provide a resin film which has a low coefficient of thermal expansion, has a sufficiently low dielectric loss tangent, and can reduce transmission loss.SOLUTION: A polyimide-based film contains (A) non-thermoplastic polyimide and (B) a polystyrene elastomer, has a phase-separation structure, and has a coefficient of thermal expansion of 50 ppm / K or less, a relative dielectric constant at 10 GHz when being measured by a split post dielectric resonator (SPDR) under environment of a temperature of 24 to 26°C and a humidity of 45 to 55% of 3.0 or less, and a dielectric loss tangent of 0.0030 or less. The polyimide-based film preferably has such a sea-island structure that the component (A) is a sea phase and the component (B) is an island phase, and with respect to the total amount of the resin component, a content ratio of the component (A) is preferably within a range of 50 to 80 wt.%, and a content ratio of the component (B) is preferably within a range of 10 to 50 wt.%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyimide film, a metal-clad laminate and a flexible circuit board utilizing the polyimide film, and a resin composition used therein. [Background technology]

[0002] In recent years, with the miniaturization, weight reduction, and space-saving of electronic devices, the demand for flexible printed circuit boards (FPCs) has increased. These boards are thin, lightweight, flexible, and possess excellent durability even after repeated bending. Because FPCs enable three-dimensional and high-density mounting even in limited spaces, their applications are expanding to include wiring, cables, connectors, and other components in electronic devices such as HDDs, DVDs, and smartphones. The material used for FPCs and other circuit boards is a metal-clad laminate, which consists of a metal layer and an insulating resin layer.

[0003] In addition to increased density, the performance of equipment has also improved, necessitating the ability to handle higher frequency transmission signals. When transmitting high-frequency signals, large transmission losses in the transmission path can lead to problems such as electrical signal loss and longer signal delays. Furthermore, with the spread of 5G communication, mobile communication devices such as smartphones transmit enormous amounts of information, requiring the adoption of methods that transmit signals in multiple frequency bands along with higher frequency transmission signals. For metal-clad laminates used in FPCs for such high-frequency signal transmission, it is effective to make the resin layer low-dielectric loss tangent and thicker in order to improve transmission loss.

[0004] To accommodate the increasing frequency of transmitted signals, a metal-clad laminate with a laminated structure has been proposed in which a thick adhesive layer is interposed between the insulating resin layers of a pair of single-sided metal-clad laminates (for example, Patent Document 1). In Patent Document 1, thermoplastic polyimide made from dimer amine (DDA) is used as the material for the adhesive layer. Thermoplastic polyimide made from dimer amine is a useful resin material as an adhesive because it is solvent-soluble, has excellent adhesion, and good handling properties. However, to cope with the advancement of high frequencies, an even lower dielectric loss tangent is required. Furthermore, since Patent Document 1 assumes a laminated structure with a thick resin layer, it has the drawback of being difficult to apply in cases where a thinner resin layer is required, such as in multilayer substrate applications or applications requiring flexibility.

[0005] On the other hand, in order to improve the dielectric properties of resin films, a resin film has been proposed in which a polystyrene elastomer with an acid value of 10 mg KOH / g or less is blended with a thermoplastic polyimide made from dimer amine (for example, Patent Document 2). However, the resin film in Patent Document 2 has too large a coefficient of thermal expansion, making it difficult to apply to a base insulating layer where dimensional stability is required. Here, the base insulating layer is a resin layer that plays a role in maintaining mechanical strength and dimensional stability in the insulating resin layer of a metal-clad laminate. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-170417 [Patent Document 2] Japanese Patent Publication No. 2022-99778 [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, the adhesive layer in Patent Document 1 has room for further improvement in dielectric properties, and the resin film in Patent Document 2 has an excessively large coefficient of thermal expansion, thus limiting its applicability. Therefore, there was a need for a resin film that could achieve both a low coefficient of thermal expansion suitable for use as a base insulating layer and a low dielectric loss tangent necessary for high-frequency signal transmission. Therefore, an object of the present invention is to provide a resin film that has a low coefficient of thermal expansion and a sufficiently low dielectric loss tangent, thereby reducing transmission loss. [Means for solving the problem]

[0008] As a result of diligent research, the inventors of this invention have discovered that the above problem can be solved by blending a specific polyimide with a polystyrene elastomer to form a phase-separated structure, and have completed the present invention. In other words, the polyimide film of the present invention comprises the following components (A) and (B); (A) Non-thermoplastic polyimide, and (B) Polystyrene elastomer, It contains a phase-separated structure, has a thermal expansion coefficient of 50 ppm / K or less, and when measured by a split-post dielectric resonator (SPDR) in an environment of 24-26°C and 45-55% humidity, the relative permittivity at 10 GHz is 3.0 or less, and the dielectric loss tangent is 0.0030 or less.

[0009] The polyimide film of the present invention may have a sea-island structure in which component (A) is the sea phase and component (B) is the island phase.

[0010] The polyimide film of the present invention may have a content of component (A) in the range of 50 to 80% by weight, and a content of component (B) in the range of 10 to 50% by weight, relative to the total amount of resin components.

[0011] In the polyimide film of the present invention, the component (A) contains an acid dianhydride residue derived from an acid dianhydride component and a diamine residue derived from a diamine component, and may contain 30 mol% or more of a diamine residue derived from a diamine component represented by the following general formula (1) with respect to all diamine residues.

[0012]

Chemical formula

[0013] In the general formula (1), R independently represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, n represents an integer of 1 to 3, and m represents an integer of 0 to 4.

[0014] In the polyimide film of the present invention, the component (A) may contain 30 mol% or more of an acid dianhydride residue derived from an acid dianhydride component represented by the following general formula (2) with respect to all acid dianhydride residues.

[0015]

Chemical formula

[0016] In the general formula (2), Ar represents a divalent group represented by any of the following.

[0017]

Chemical formula

[0018] Here, R independently represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a halogen atom, n1 represents an integer of 1 or 2, and m represents an integer of 0 to 4.

[0019] The resin composition of the present invention comprises the following component (A1) and component (B); (A1) Polyamic acid, and (B) Polystyrene elastomer It contains the above, and the content of component (A1) is within the range of 50-80% by weight and the content of component (B) is within the range of 10-50% by weight relative to the total amount of resin components. Furthermore, in the resin composition of the present invention, component (A1) contains an acid dianhydride residue derived from an acid dianhydride component and a diamine residue derived from a diamine component, and also contains 30 mol% or more of a diamine residue derived from the diamine component represented by the above general formula (1) relative to the total number of diamine residues.

[0020] In the resin composition of the present invention, component (A1) may contain 30 mol% or more of acid dianhydride residues derived from the acid dianhydride component represented by the above general formula (2) with respect to the total acid dianhydride residues.

[0021] The present invention relates to a method for manufacturing a metal-clad laminate comprising an insulating resin layer and a metal layer provided on at least one surface of the insulating resin layer, The present invention is characterized by comprising the step of coating the above-mentioned resin composition onto the metal layer or onto a base layer provided on the metal layer, and then performing a heat treatment.

[0022] The metal-clad laminate of the present invention comprises an insulating resin layer and a metal layer provided on at least one surface of the insulating resin layer, The insulating resin layer is characterized by including a layer made of any of the polyimide-based films described above.

[0023] The flexible circuit board of the present invention comprises an insulating resin layer and a wiring layer provided on at least one surface of the insulating resin layer, The insulating resin layer is characterized by including a layer made of any of the polyimide-based films described above. [Effects of the Invention]

[0024] The polyimide film of the present invention contains components (A) and (B) and has a phase-separated structure, thereby achieving both a low coefficient of thermal expansion and a low dielectric loss tangent. Therefore, the polyimide film of the present invention can be applied as a base insulating layer where dimensional stability is required, and can also be used in multilayer substrate applications and applications requiring flexibility by thinning the film. A flexible circuit board using the polyimide film of the present invention can reduce the transmission loss of high-frequency signals while maintaining excellent dimensional stability. [Modes for carrying out the invention]

[0025] Next, embodiments of the present invention will be described.

[0026] [Polyimide film] The polyimide film of the present invention comprises the following components (A) and (B); (A) Non-thermoplastic polyimide, and (B) Polystyrene elastomer, It contains and has a phase-separated structure composed of component (A) and component (B).

[0027] <(A) component> The component (A) used in this invention is a non-thermoplastic polyimide. In this invention, "non-thermoplastic polyimide" means a polyimide with a storage modulus of 1.0 × 10⁻¹⁶ at 30°C, as measured using a dynamic viscoelasticity analyzer (DMA). 9 The storage modulus is 1.0 × 10⁻¹⁰ in the temperature range where the storage modulus is above Pa and within 30°C of the glass transition temperature. 8 This refers to materials exhibiting a Pa or higher storage modulus. Furthermore, "thermoplastic polyimide" refers to materials with a storage modulus of 1.0 × 10⁻¹⁶ at 30°C, as measured using a dynamic viscoelasticity analyzer (DMA). 9 The storage modulus is 1.0 × 10⁻¹⁰ in the temperature range where the storage modulus is above Pa and within 30°C of the glass transition temperature. 8This refers to values ​​less than Pa. In this invention, "polyimide" refers to resins made of polymers having imide groups in their molecular structure, including polyimide, polyamideimide, polyetherimide, polyesterimide, polysiloxaneimide, and polybenzimidazoleimide.

[0028] Non-thermoplastic polyimides are obtained by imidizing the precursor polyamic acid. Polyamic acid is obtained by reacting a specific acid dianhydride component with a specific diamine component. Therefore, non-thermoplastic polyimides and their precursor polyamic acid contain acid dianhydride residues derived from the acid dianhydride component and diamine residues derived from the diamine component. Here, an acid dianhydride residue refers to a tetravalent group derived from an acid dianhydride, and a diamine residue refers to a divalent group derived from a diamine compound. When the raw materials, the acid dianhydride component and the diamine component, are reacted in nearly equimolar amounts, the types and molar ratios of acid dianhydride residues and diamine residues contained in the polyimide can be approximated to the types and molar ratios of the raw materials. The following describes the acid dianhydride residues and diamine residues contained in the non-thermoplastic polyimide of component (A), along with their raw materials.

[0029] The non-thermoplastic polyimide of component (A) contains 30 mol% or more of acid dianhydride residues derived from the acid dianhydride component represented by the following general formula (2), relative to the total number of acid dianhydride residues. Hereinafter, the acid dianhydride residues derived from the acid dianhydride represented by general formula (2) may be referred to as "acid dianhydride residue (2)".

[0030] [ka]

[0031] In general formula (2), Ar represents a divalent group that can be represented in any of the following ways.

[0032] [ka]

[0033] Here, R independently represents an alkyl group having 1 to 3 carbon atoms, which may be substituted with a halogen atom; n1 represents an integer of 1 or 2; and m represents an integer of 0 to 4.

[0034] The acid dianhydride represented by general formula (2) has a phenyl, biphenyl, or naphthalene skeleton as the group Ar within the molecule, and further has two ester structures (-CO-O-) bonded to these phenyl, biphenyl, or naphthalene skeletons. The phenyl, biphenyl, and naphthalene skeletons are rigid, and the ester structures have the effect of conferring an ordered structure to the entire polymer. Therefore, by including the acid dianhydride residue (2), it is possible to reduce the coefficient of thermal expansion (low CTE), and to effectively reduce the dielectric loss tangent (low dielectric loss tangent) by improving the ordered structure of the molecule and suppressing its motion. As the substituent R in general formula (2), a methyl group is preferred, for example.

[0035] Preferred examples of acid dianhydrides represented by general formula (2) include 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ), p-biphenylenebis(trimellitic acid monoester acid dihydrate) (BP-TME, CAS number; 10340-81-5), 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl=bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (TMPBP-TME, CAS number; 1042278-26-1), and 2,6-naphthalenebis(trimellitic acid monoester acid dianhydride) (26DHN-TME, CAS number; 115383-00-1).

[0036] The content of acid dianhydride residue (2) in the non-thermoplastic polyimide of component (A) is 30 mol% or more relative to the total acid dianhydride residues, preferably in the range of 30 to 100 mol%, and more preferably in the range of 50 to 90 mol%. If the content of acid dianhydride residue (2) is less than 30 mol%, the effects of both low dielectric loss tangent and low CTE will not be fully exhibited. The upper limit of the content of acid dianhydride residue (2) may be 100 mol%, but when other acid dianhydrides are used in combination for the purpose of imparting arbitrary functionality, the amount of acid dianhydride represented by general formula (2) can be adjusted according to the amount used.

[0037] The non-thermoplastic polyimide of component (A) may contain residues of acid dianhydrides commonly used as raw materials for polyimides, in addition to residues derived from the acid dianhydride represented by the general formula (2) above, to the extent that the effects of the invention are not impaired. Preferred acid dianhydride residues include, for example, acid dianhydride residues derived from 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA residues) and acid dianhydride residues derived from pyromellitic acid dianhydride (PMDA residues). BPDA residues are preferred because they are rigid, making it easy to form an ordered polymer structure and reducing the dielectric loss tangent by suppressing molecular motion. PMDA residues are preferred because they are structurally excellent in planarity and rigidity, and can increase the stacking ability between molecular chains, thereby lowering the dielectric loss tangent of the polyimide and reducing CTE.

[0038] The non-thermoplastic polyimide of component (A) contains acid dianhydride residues (2) derived from acid dianhydride represented by general formula (2), which have two ester structures (-CO-O-) in the molecule, as its main constituent units, and is therefore characterized by a relatively high ester group concentration. From the viewpoint of imparting an ordered structure to the entire polymer and reducing the dielectric loss tangent, the ester group concentration in component (A) is preferably in the range of 3 to 15% by weight, and more preferably in the range of 7 to 15% by weight. Here, the ester group concentration can be calculated by the proportion of ester groups (-COO-) in the total molecular weight of the polyimide structure.

[0039] The non-thermoplastic polyimide of component (A) contains 30 mol% or more of diamine residues derived from the diamine component represented by the following general formula (1), relative to the total number of diamine residues. Hereinafter, the diamine residue derived from the diamine compound represented by general formula (1) may be referred to as "diamine residue (1)". Note that in general formula (1), the hydrogen atoms in the two terminal amino groups may be substituted, for example, -NR x R y (Here, R x ,R y (This may independently mean any substituent such as an alkyl group.)

[0040] [ka]

[0041] In general formula (1), R independently represents an alkyl group having 1 to 3 carbon atoms, which may be substituted with a halogen atom; n represents an integer from 1 to 3; and m represents an integer from 0 to 4.

[0042] The diamine residue (1) has a rigid structure and therefore contributes to the conferring of an ordered structure to the entire polymer. Specifically, the diamine residue (1) can improve the stacking properties between molecular chains by improving the planarity and rigidity of the polyimide molecular skeleton. As a result, it is possible to reduce the mobility of the diamine residue, thereby lowering the dielectric loss tangent of the polyimide film and lowering the coefficient of thermal expansion. Furthermore, when the diamine residue (1) contains a biphenyl skeleton or a terphenyl skeleton, the effect of conferring an ordered structure to the entire polymer is amplified, and the molecular weight of monomer-derived units can be increased, making it possible to reduce the imide group concentration, which in turn also reduces the dielectric loss tangent. As the substituent R in general formula (1), for example, a methyl group or a methyl group substituted with a halogen atom is preferred, and as the halogen atom, a fluorine atom is preferred.

[0043] Preferred examples of diamine compounds represented by general formula (1) include 1,4-diaminobenzene (p-PDA), 4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 2,2'-di-n-propyl-4,4'-diaminobiphenyl (m-NPB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl ( Examples include TFMB and 4,4"-diamino-p-terphenyl (DATP). Among these, 1,4-diaminobenzene (p-PDA), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), and 4,4"-diamino-p-terphenyl (DATP) are particularly preferred because they have a significant effect in conferring an ordered structure to the entire polymer and significantly reduce dielectric loss tangent by lowering the imide group concentration.

[0044] The content of diamine residue (1) in the non-thermoplastic polyimide of component (A) is 30 mol% or more relative to the total number of diamine residues, preferably in the range of 60 to 100 mol%, and more preferably in the range of 70 to 100 mol%. If the content of diamine residue (1) is less than 30 mol%, the effect of reducing the dielectric loss tangent is not sufficiently exhibited. Furthermore, from the viewpoint of reducing the dielectric loss tangent, it is preferable to make the proportion of diamine residue (1) among all diamine residues as large as possible, and the content of diamine residue (1) may be 100 mol%.

[0045] The non-thermoplastic polyimide of component (A) preferably contains, in addition to the above-mentioned diamine residue (1), a diamine residue derived from a diamine compound having a bulky molecular structure. Examples of diamine compounds having a bulky molecular structure include 2,6-diamino-3,5-diethyltoluene, 2,4-diamino-3,5-diethyltoluene, 2,4-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, bis(4-amino-3-ethyl-5-methylphenyl)methane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP). Because these diamine compounds have a bulky molecular structure, when used in combination with the diamine compound represented by general formula (1), the diffusion efficiency of organic solvents from the polyimide film is increased when forming a polyimide film by the casting method, foaming is suppressed, and the heat treatment time for thermal imidization can be shortened. From this viewpoint and from the viewpoint of reducing CTE, component (A) preferably contains a total of diamine residues derived from the above-mentioned bulky molecular structure diamine compound in the range of 1 to 50 mol%, more preferably in the range of 5 to 50 mol%, and most preferably in the range of 5 to 40 mol%, relative to the total number of diamine residues.

[0046] The non-thermoplastic polyimide of component (A) may contain, in addition to the diamine residues derived from the above-mentioned diamine compound, residues of diamine compounds commonly used as raw materials for polyimides, to the extent that the effects of the invention are not impaired.

[0047] In the non-thermoplastic polyimide of component (A), the hygroscopicity, dielectric properties, thermal expansion coefficient, storage modulus, tensile modulus, etc., can be controlled by selecting the types of acid dianhydride residues and diamine residues, and the molar ratio of each when two or more acid dianhydride residues or diamine residues are included. In the non-thermoplastic polyimide of component (A), if there are multiple structural units, they may exist as blocks or randomly, but random arrangement is preferred.

[0048] Furthermore, in the non-thermoplastic polyimide of component (A), it is preferable that the acid dianhydride residues and diamine residues consist of aromatic acid dianhydride residues derived from aromatic tetracarboxylic dianhydrides and aromatic diamine residues derived from aromatic diamines. By making the acid dianhydride residues and diamine residues contained in the polyamic acid and polyimide all residues having aromatic groups, the dimensional accuracy of the polyimide film under high-temperature conditions can be improved.

[0049] The non-thermoplastic polyimide of component (A) can be produced by reacting an acidic dianhydride and a diamine compound in a solvent to produce polyamic acid, a precursor of polyimide, and then heating and cyclizing (imidization). For example, polyamic acid can be obtained by dissolving an acidic dianhydride and a diamine compound in an approximately equimolar amount in an organic solvent and allowing a polymerization reaction to occur by stirring at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours. In the reaction, the reactants are dissolved in the organic solvent in a range of 5 to 30% by weight, preferably 10 to 20% by weight, to produce the precursor. Examples of organic solvents used in polymerization reactions include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and cresol. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used. There are no particular restrictions on the amount of such organic solvents used, but it is preferable to adjust the amount used so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 30% by weight. The synthesized polyamic acid is usually advantageous to use as a reaction solvent solution, but it can be concentrated, diluted, or replaced with other organic solvents as needed.

[0050] The method for imidizing polyamic acid is not particularly limited, and a heat treatment such as heating at a temperature in the range of 80 to 400°C for 1 to 24 hours is preferably employed.

[0051] The weight-average molecular weight of the non-thermoplastic polyimide component (A) is preferably in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the strength of the film tends to decrease and it becomes more prone to embrittlement. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during the coating process.

[0052] <(B) component> Component (B) is a polystyrene elastomer. The polystyrene elastomer is a copolymer of styrene or a derivative thereof and a conjugated diene compound, and includes a hydrogenated version thereof. Here, the styrene or its derivative is not particularly limited, but examples include styrene, methylstyrene, butylstyrene, divinylbenzene, vinyltoluene, etc. The conjugated diene compound is not particularly limited, but examples include butadiene, isoprene, 1,3-pentadiene, etc. The polystyrene elastomer is preferably hydrogenated. Hydrogenation improves its thermal stability, makes it less susceptible to degradation such as decomposition and polymerization, and enhances its aliphatic properties, thereby improving its compatibility with other resin components.

[0053] The copolymer structure of component (B) polystyrene elastomer may be a block structure or a random structure. Preferred specific examples of polystyrene elastomers include, but are not limited to, styrene-butadiene-styrene block copolymer (SBS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene·propylene-styrene block copolymer (SEEPS).

[0054] The weight-average molecular weight of the polystyrene elastomer component (B) is not particularly limited, but is preferably in the range of 50,000 to 300,000, more preferably in the range of 50,000 to 270,000, and most preferably in the range of 50,000 to 150,000. If the weight-average molecular weight of component (B) exceeds 300,000, the viscosity of the resin composition mixed with component (A) will increase, making it difficult to form a film, and if it falls below 50,000, the hygroscopicity of the polyimide film will increase, making it difficult to stably maintain a low dielectric loss tangent.

[0055] The acid value of the polystyrene elastomer in component (B) is preferably 10 mg KOH / g or less, more preferably 1 mg KOH / g or less, and even more preferably 0 mg KOH / g. By using a polystyrene elastomer with an acid value of 10 mg KOH / g or less, the dielectric loss tangent when a polyimide-based film is formed can be reduced. On the other hand, if the acid value exceeds 10 mg KOH / g, the dielectric properties deteriorate due to the increase in polar groups. Therefore, the lower the acid value, the better, and an acid-unmodified polystyrene elastomer (i.e., one with an acid value of 0 mg KOH / g) is most suitable as component (B) of the present invention.

[0056] The polystyrene elastomer of component (B) preferably has a styrene unit [-CH2CH(C6H5)-] content of 10% to 65% by weight, more preferably 20% to 65% by weight, and most preferably 30% to 60% by weight. If the styrene unit content in the polystyrene elastomer is less than 10% by weight, the elastic modulus of the resin decreases and the handling properties of the film deteriorate. If it exceeds 65% by weight, the amount of rubber component in the polystyrene elastomer decreases, which leads to a deterioration of dielectric properties. Furthermore, because the styrene unit content is within the above range, the proportion of aromatic rings in the polyimide film is increased. This makes it possible to enhance the absorption in the ultraviolet region when forming via holes (through holes) and blind via holes by laser processing during the manufacturing of flexible circuit boards using polyimide films, thereby improving laser processability.

[0057] (B) As the polystyrene elastomer, commercially available products can be appropriately selected and used. As such commercially available polystyrene elastomers, for example, A1535HU (product name), G1652MU (product name), G1726VS (product name), G1645VS (product name), FG1901GT (product name), G1650MU (product name), G1654HU (product name), G1730VO (product name), MD1653MO (product name), etc., manufactured by KRATON, can be preferably used.

[0058] In addition to components (A) and (B), the polyimide film of this embodiment may contain, as necessary, inorganic fillers, organic fillers, plasticizers, curing accelerators, coupling agents, pigments, flame retardants, etc., as long as they do not impair the effects of the invention. Examples of inorganic fillers include silicon dioxide, aluminum oxide, beryllium oxide, niobium oxide, titanium oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, magnesium fluoride, potassium silicofluoride, metal phosphinate, etc. These can be used individually or in mixtures of two or more. Furthermore, resin components other than components (A) and (B) may be included, as long as they do not impair the effects of the invention.

[0059] In the polyimide film of this embodiment, the content ratio of component (A) to the total amount of resin components is preferably in the range of 50 to 80% by weight, and more preferably in the range of 50 to 70% by weight. If the content of component (A) to the total amount of resin components is less than 50% by weight, the thermal expansion coefficient of the polyimide film may increase, impairing its dimensional stability. On the other hand, if the content of component (A) exceeds 80% by weight, the effect of reducing the dielectric loss tangent will not be sufficiently exhibited.

[0060] In the polyimide film of this embodiment, the content ratio of component (B) to the total amount of resin components is preferably in the range of 10 to 50% by weight, and more preferably in the range of 30 to 50% by weight. If the content of component (B) to the total amount of resin components is less than 10% by weight, the effect of reducing the dielectric loss tangent of the polyimide film may not be sufficiently exhibited. On the other hand, if the content of component (B) exceeds 50% by weight, the thermal expansion coefficient of the polyimide film may increase, impairing its dimensional stability.

[0061] Furthermore, the total content of component (A) and component (B) relative to the entire polyimide film is preferably 50% by weight or more, more preferably 60 to 100% by weight, and most preferably 70 to 100% by weight.

[0062] <Phase separation structure> In this embodiment, it is important that the polyimide film has a phase separation structure in order to achieve both a low coefficient of thermal expansion and a low dielectric loss tangent. Specifically, it is preferable to have a sea-island structure in which component (A) is the sea phase and component (B) is the island phase. In this way, by making the sea phase component (A), the CTE of the entire polyimide film can be reduced, while the dielectric loss tangent can be reduced by the island phase component (B). Furthermore, the volume ratio of the sea phase to the island phase (sea phase:island phase) is not particularly limited, but as an example, it is preferable to have a range of 80:20 to 50:50. The volume ratio of the sea phase to the island phase can be determined by assuming a uniform phase separation structure and considering the area ratio of the sea phase to the island phase as the volume ratio when observing the cross-section in the thickness direction of the polyimide film using an electron microscope (SEM). By forming such a phase separation structure, the physical properties do not become a simple average of the two components, and it is possible to achieve low induced tangent reduction by component (B) while maintaining the low CTE characteristics derived from component (A).

[0063] <Coefficient of thermal expansion (CTE)> The polyimide film of this embodiment, when applied, for example, as an insulating resin layer for a flexible circuit board, has a coefficient of thermal expansion (CTE) of 50 ppm / K or less, preferably in the range of 1 ppm / K to 30 ppm / K, and more preferably in the range of 10 ppm / K to 25 ppm / K, in order to prevent warping and a decrease in dimensional stability. If the coefficient of thermal expansion (CTE) of the polyimide film exceeds 50 ppm / K, warping may occur or dimensional stability may decrease.

[0064] <Dielectric loss tangent> The polyimide film of this embodiment, when applied, for example, as an insulating resin layer in a flexible circuit board, has a dielectric loss tangent (Tanδ) at 10 GHz of 0.0030 or less, preferably 0.0025 or less, and more preferably 0.0020 or less, when measured by a split-post dielectric resonator (SPDR) in an environment of 24-26°C and 45-55% humidity, in order to reduce dielectric loss during high-frequency signal transmission. In order to improve the transmission loss of a flexible circuit board, it is important to control the dielectric loss tangent of the insulating resin layer, and the effect of reducing transmission loss is greatly increased when the dielectric loss tangent (Tanδ) of the polyimide film at 10 GHz is 0.0030 or less. Therefore, when a polyimide film is applied as an insulating resin layer (preferably a base insulating layer) in a high-frequency flexible circuit board, transmission loss can be efficiently reduced. When the dielectric loss tangent at 10 GHz exceeds 0.0030, problems such as increased electrical signal loss in the high-frequency signal transmission path are likely to occur when polyimide-based films are used as insulating resin layers in flexible circuit boards.

[0065] <Relative permittivity> In this embodiment, when the polyimide film is applied, for example, as an insulating resin layer in a flexible circuit board, the relative permittivity at 10 GHz measured by a split post dielectric resonator (SPDR) in an environment of 24-26°C and 45-55% humidity is 3.0 or less, preferably 2.8 or less, in order to ensure impedance matching. If the relative permittivity at 10 GHz exceeds 3.0, when the polyimide film is applied as an insulating resin layer in a flexible circuit board, it leads to a deterioration of dielectric loss, which can easily cause problems such as increased electrical signal loss in the high-frequency signal transmission path.

[0066] <Thickness> The thickness of the polyimide film in this embodiment is not particularly limited and can be set appropriately depending on the purpose, but for flexible circuit board applications, for example, a range of 5 to 60 μm is preferred, and a range of 15 to 50 μm is more preferred.

[0067] <Lamination configuration of polyimide films> The polyimide film according to this embodiment can be used as part of or as part of a resin film containing a single or multiple resin layers. Preferably, the main layer of the resin film is the polyimide film according to this embodiment. Here, "main layer" means a layer that accounts for more than 50%, preferably 60-100%, of the total thickness of the resin film. The polyimide film that is the main layer functions as a base insulating layer that plays a role in maintaining the mechanical strength and dimensional stability of the resin film. By having the polyimide film according to this embodiment as the main layer, it is possible to lower the dielectric loss tangent and CTE of the entire resin film. Such a resin film may be a film (sheet) made only of insulating resin, or it may be laminated on a substrate such as a metal foil such as copper foil or a glass plate.

[0068] [Resin composition] The resin composition of one embodiment of the present invention comprises the following components (A1) and (B); (A1) Polyamic acid, and (B) Polystyrene elastomer, It contains the following. Here, the polyamic acid of component (A1) is a precursor of the non-thermoplastic polyimide of component (A). The types and ratios of acid dianhydride residues and diamine residues contained in the polyamic acid of component (A1), and the synthesis conditions of the polyamic acid, are as described for component (A).

[0069] The content of component (A1) relative to the total amount of resin components in the resin composition is in the range of 50 to 80% by weight, and preferably in the range of 50 to 70% by weight. If the content of component (A1) relative to the total amount of resin components is less than 50% by weight, the coefficient of thermal expansion may increase when a polyimide film is formed, impairing dimensional stability. On the other hand, if the content of component (A1) exceeds 80% by weight, the effect of reducing the dielectric loss tangent may not be sufficiently obtained when a polyimide film is formed.

[0070] The content of component (B) relative to the total amount of resin components in the resin composition is in the range of 10 to 50% by weight, and preferably in the range of 30 to 50% by weight. If the content of component (B) relative to the total amount of resin components is less than 10% by weight, the effect of reducing the dielectric loss tangent may not be sufficiently exhibited when a polyimide film is formed. On the other hand, if the content of component (B) exceeds 50% by weight, the coefficient of thermal expansion may increase when a polyimide film is formed, impairing dimensional stability, and the solid content concentration in the resin composition may become too high, increasing viscosity and reducing handling properties.

[0071] In the resin composition, the total content of components (A1) and (B) relative to the total solid content including the resin component is preferably 50% by weight or more, more preferably 60-100% by weight, and most preferably 70-100% by weight. The solid content in the resin composition refers to the total of the components excluding the solvent.

[0072] The resin composition may contain a solvent such as an organic solvent. Since the polyamic acid in component (A1) is soluble in polar organic solvents, and the polystyrene elastomer in component (B) shows good solubility in non-polar solvents, it is preferable to prepare the resin composition as a resin solution (varnish) containing a solvent. (A1) Suitable polar organic solvents for the polyamic acid of component (A1) include, for example, one or more selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglime, cresol, etc. As a nonpolar solvent suitable for the polystyrene elastomer of component (B), one or more selected from, for example, xylene, toluene, and benzene can preferably be used. Therefore, it is preferable to use a mixed solvent containing the above polar organic solvent and the above nonpolar solvent in a predetermined ratio in the resin composition. The mixing ratio of the polar organic solvent and the nonpolar solvent has a range depending on the blending ratio of component (A1) and component (B), but when the weight ratio of component (A1) and component (B) is within the above range, it is preferable to have a solvent mixing ratio (polar organic solvent:nonpolar solvent) in the range of 90:10 to 40:60, and more preferably in the range of 80:20 to 50:50.

[0073] While there are no particular restrictions on the solvent content in the resin composition, it is preferable to adjust the amount so that the total content of polyamic acid (component A1) and component (B) relative to the entire composition is approximately 5 to 30% by weight. The viscosity of the resin composition is preferably in the range of 3,000 cps to 100,000 cps, and more preferably in the range of 5,000 cps to 50,000 cps, as this range enhances handling when coating the resin composition and facilitates the formation of a coating film of uniform thickness. If the viscosity falls outside the above range, defects such as uneven thickness and streaks are more likely to occur in the film during coating operations using a coater or the like.

[0074] The resin composition may further contain optional components, such as organic fillers, inorganic fillers, cyclizing agents, imidation catalysts, curing agents, plasticizers, coupling agents, pigments, flame retardants, and heat dissipation agents, to the extent that they do not impair the effects of the invention. In addition, it may contain resin components other than components (A) and (B), to the extent that they do not impair the effects of the invention.

[0075] The resin composition can be prepared, for example, by blending a polyamic acid solution of component (A1), prepared using any solvent, with polystyrene elastomer component (B) and mixing them. At this time, it is preferable to uniformly mix the polyamic acid and polystyrene elastomer using, for example, an MS stirrer. Alternatively, the polystyrene elastomer may be mixed in a dissolved state in the solvent, or a solvent that exhibits high solubility for the polystyrene elastomer may be added. In the mixed state of components (A1) and (B), it is preferable to adjust the content ratio of the polar organic solvent and the aromatic hydrocarbon solvent to a predetermined ratio.

[0076] [Method for manufacturing polyimide films] The polyimide film of this embodiment is, for example, obtained in the following steps 1a to 1c; (1a) A step of applying the above resin composition to a support substrate and drying it, (1b) A step of forming a polyimide film by heat-treating the coating on a support substrate to imide the polyamic acid of component (A1), (1c) A step of obtaining a polyimide film by separating the support substrate and the polyimide film, This can be manufactured by carrying out the following. In this way, by imidizing the resin composition coating film while it is fixed to the support substrate, changes in expansion and contraction of the polyimide film during the imidization process can be suppressed, and the thickness and dimensional accuracy of the polyimide film can be maintained. There are no particular restrictions on the method of applying the resin composition to the support substrate; for example, it can be applied using a coater such as a comma, die, knife, or lip.

[0077] [Metal-clad laminate] A metal-clad laminate according to one embodiment of the present invention is a metal-clad laminate comprising an insulating resin layer and a metal layer laminated on one or both sides thereof, wherein at least one layer of the insulating resin layer is the polyimide film described above. The insulating resin layer may be a single layer consisting only of a polyimide film, or it may have multiple layers in which other resin layers are laminated on a polyimide film layer. In the case of multiple layers, it is preferable that the polyimide film layer is the main layer of the insulating resin layer. Here, "main layer" means a layer that accounts for more than 50%, preferably 60-100%, of the total thickness of the insulating resin layer.

[0078] A preferred embodiment of the metal-clad laminate is one in which the insulating resin layer has a plurality of polyimide layers, including a polyimide layer (X) in contact with the metal layer and a polyimide-based resin layer (Y) laminated on the polyimide layer (X), and the main polyimide-based resin layer (Y) is a layer made of the polyimide-based film. The main polyimide-based resin layer (Y) functions as a base insulating layer that plays a role in maintaining the mechanical strength and dimensional stability of the insulating resin layer. By having a polyimide-based resin layer (Y) with a low coefficient of thermal expansion (CTE) and a low dielectric loss tangent, such a metal-clad laminate can improve the dimensional stability of the entire insulating resin layer and achieve a low dielectric loss tangent. In this case, the metal-clad laminate may have any additional resin layer laminated on top of the polyimide-based resin layer (Y).

[0079] The polyimide constituting the underlying polyimide layer (X) is preferably a thermoplastic polyimide to ensure adhesion to the metal layer. Here, a common thermoplastic polyimide used in circuit boards can be applied. From the viewpoint of ensuring adhesive function, the thickness of the polyimide layer (X) is preferably in the range of 1 μm to 15 μm, and more preferably in the range of 2 μm to 10 μm. If the thickness of the polyimide layer (X) is less than the lower limit, the adhesion will be insufficient, and if it exceeds the upper limit, dimensional stability tends to deteriorate.

[0080] The thickness of the polyimide resin layer (Y) is preferably in the range of 6 μm to 50 μm, and more preferably in the range of 9 μm to 40 μm, from the viewpoint of ensuring its function as a base insulating layer and ease of transport during manufacturing. If the thickness of the polyimide resin layer (Y) is less than the lower limit, electrical insulation and handling will be insufficient, and if it exceeds the upper limit, productivity will decrease. The polyimide resin layer (Y) should have a thickness of more than 50%, preferably 60% or more, of the total thickness of the insulating resin layer.

[0081] The metal layer constituting the metal-clad laminate of this embodiment is not particularly limited, but examples include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper or copper alloys are particularly preferred. The material of the wiring layer in the flexible circuit board, which will be described later, is the same as that of the metal layer.

[0082] The thickness of the metal layer is not particularly limited, but when using metal foil such as copper foil, it is preferably 35 μm or less, and more preferably in the range of 5 μm to 25 μm. From the viewpoint of production stability and handling, it is preferable that the lower limit of the metal foil thickness be 5 μm. When using copper foil, either rolled copper foil or electrolytic copper foil may be used. In addition, commercially available copper foil can be used as the copper foil.

[0083] Furthermore, the ten-point average roughness (Rzjis) of the surface of the metal layer in contact with the polyimide layer (X) is preferably 1.2 μm or less, and more preferably 1.0 μm or less. When the metal layer is made from metal foil, setting the surface roughness Rzjis to 1.2 μm or less enables fine wiring processing to accommodate high-density mounting, and reduces transmission loss during high-frequency signal transmission, thus making it applicable to flexible circuit boards for high-frequency signal transmission. In addition, the metal layer may be surface-treated with, for example, siding, aluminum alkoxide, aluminum chelate, or silane coupling agent for purposes such as rust prevention or improved adhesion.

[0084] The metal-clad laminate of this embodiment can be manufactured according to conventional methods. If the insulating resin layer is a single layer, for example, it can be manufactured by using metal foil as a support substrate in steps 1a and 1b described in the method for manufacturing the polyimide film described above.

[0085] Furthermore, if the insulating resin layer has multiple polyimide layers, including a polyimide layer (X) in contact with the metal layer and a polyimide-based resin layer (Y) laminated on the polyimide layer (X), the following methods [1] and [2] can be exemplified. [1] A method for producing a metal-clad laminate by applying a resin solution to a metal foil that will form a metal layer, drying it, and then heat-treating it to imide polyamic acid to form an insulating resin layer containing a polyimide-based resin layer (Y). [2] A method for producing a metal-clad laminate by applying multiple types of resin solutions to a metal foil that will form a metal layer, simultaneously laminating them in multiple layers by multilayer extrusion, drying the mixture, and then heat-treating the entire mixture to imide the polyamic acid and form an insulating resin layer containing a polyimide resin layer (Y) (hereinafter referred to as the multilayer extrusion method).

[0086] The method described in [1] above, for example, involves the following steps (i), (ii): (i) A step of applying a resin solution onto a metal foil or onto a base layer laminated on a metal foil and drying it, (ii) A step of heat-treating the coating film on a metal foil to imide the polyamic acid, It can include... In the method of [1], the resin solution can be a polyimide solution or its precursor solution that constitutes the polyimide layer (X), a resin composition for forming the polyimide-based resin layer (Y), or a resin solution for forming any resin layer. Then, by repeating steps (i) and (ii) with different types of resin solutions, or by repeating step (i) and then performing step (ii) all at once, an insulating resin layer can be formed on the metal foil. In this case, the coating film of the polyimide layer (X) or its precursor becomes the base layer. There are no particular restrictions on the method of applying the resin solution to the metal foil or the base layer, and it can be applied using coaters such as commas, dies, knives, or lips.

[0087] The method described in [2] above involves simultaneously applying a resin solution of a polyimide precursor constituting the polyimide layer (X), a resin composition for forming a polyimide-based resin layer (Y), and, if necessary, a resin solution for forming an additional resin layer, by multilayer extrusion, drying, and then performing imidization by heat treatment in the same manner as in step (ii) of the method described in [1] above.

[0088] In the metal-clad laminate manufactured by the above method, the imidization of polyamic acid is completed on the metal foil, so that the resin composition coating is fixed to the metal foil or substrate layer during imidization. This suppresses expansion and contraction changes of the polyimide resin layer (Y) during the imidization process, and maintains the thickness and dimensional accuracy of the insulating resin layer.

[0089] [Flexible circuit board] The metal-clad laminate of the present invention is mainly useful as a circuit board material for FPCs and the like. By processing the metal layer of the metal-clad laminate into a pattern using conventional methods to form a wiring layer, a flexible circuit board, which is one embodiment of the present invention, can be manufactured. A flexible circuit board in which the metal layer of the metal-clad laminate of the present invention is processed into wiring is also one embodiment of the present invention. That is, the flexible circuit board of the present embodiment includes an insulating resin layer including a single layer or a plurality of layers, and a wiring layer provided on at least one surface of the insulating resin layer, and the insulating resin layer may include the polyimide-based resin layer (Y). Further, in order to enhance the adhesion between the insulating resin layer and the wiring layer, the layer in the insulating resin layer that contacts the wiring layer is preferably the polyimide layer (X).

Example

[0090] Examples are shown below to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples. In the following examples, unless otherwise specified, various measurements and evaluations are as follows.

[0091] [Measurement of coefficient of thermal expansion (CTE)] A polyimide film with a size of 3 mm × 20 mm was heated from 30°C to 170°C at a rate of 20°C / min at a constant heating rate while applying a load of 5.0 g using a TMA (manufactured by Hitachi High-Tech Corporation, product name; TMA / SS6000), and then held at that temperature for 10 minutes, and then cooled at a rate of 5°C / min. The average coefficient of thermal expansion (coefficient of thermal expansion) from 150°C to 50°C was determined.

[0092] [Measurement of storage elastic modulus] The storage elastic modulus was measured using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments Japan Co., Ltd., product name; RSA-G2) for a sample film with a size of 5 mm × 20 mm at a heating rate of 10°C / min from 25°C to 350°C and a frequency of 1 Hz. The temperature at which the elastic modulus change (tanδ) was maximum was defined as the glass transition temperature. The storage elastic modulus at 30°C measured using DMA is 1.0×10 9 Pa or more, and the storage elastic modulus in the temperature range within the glass transition temperature + 30°C is 1.0×10 8 Pa or more is defined as "non-thermoplastic", and the storage elastic modulus at 30°C measured using a dynamic viscoelasticity measuring device (DMA) is 1.0×10 9 Pa or more, and the storage elastic modulus in the temperature range within the glass transition temperature + 30°C is 1.0×108 Materials with a Pa value less than Pa were defined as "thermoplastic."

[0093] [Measurement of relative permittivity and dielectric loss tangent] The relative permittivity Dk and dielectric loss tangent Df of a resin sheet at 10 GHz were measured using a vector network analyzer (Agilent, product name E8363C) and an SPDR resonator. The material used for the measurement was left standing for 24 hours under conditions of temperature 24-26°C and humidity 45-55%RH.

[0094] [Viscosity measurement] Viscosity was measured at 25°C using an E-type viscometer (Brookfield, product name: DV-II+Pro). The rotation speed was set so that the torque was between 10% and 90%, and the value was read after 2 minutes had elapsed since the start of measurement, when the viscosity had stabilized.

[0095] [Measurement of weight-average molecular weight (Mw)] The weight-average molecular weight was measured using gel permeation chromatography (HLC-8220GPC, manufactured by Tosoh Corporation). Polystyrene was used as the standard substance, and tetrahydrofuran (THF) was used as the developing solvent.

[0096] [Confirmation of phase separation structure] A resin film was cut with a single blade, embedded in epoxy resin, and then the cross-section of the film was exposed by mechanical polishing. Subsequently, osmium vapor deposition was performed to prepare a sample for cross-sectional observation with a width of approximately 7 mm. Cross-sectional observation of this sample in the thickness direction was performed using a scanning electron microscope (SEM; JEOL Ltd., product name; JSM-7900F) equipped with an energy-dispersive X-ray spectrometer (EDX detector; Oxford Corporation, product name; Extreme). The measurement conditions were as follows. SEM measurement conditions: Acceleration voltage: 5kV, Irradiation current: 12μA EDX measurement conditions: Acceleration voltage: 5kV, Irradiation current: 10μA A structure in which island portions, primarily composed of one component, are scattered within a sea portion, primarily composed of the other component, was identified as a sea-island structure. Elemental mapping using EDX was performed to determine the classification of the sea portion and island portion. The sea portion, where nitrogen components were detected, was assigned to the non-thermoplastic polyimide portion, while the island portion, where nitrogen components were not detected, was assigned to the polystyrene elastomer portion.

[0097] The abbreviations used in this example indicate the following compounds. BP-TME: p-biphenylenebis(trimellitic acid monoester anhydride), CAS Number; 10340-81-5) BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride PMDA: Pyromelit acid dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane Bisaniline M: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene NMP:N-methyl-2-pyrrolidone Polystyrene elastomer: Manufactured by KRATON, product name: G1652MU (hydrogenated polystyrene elastomer, styrene unit content 30% by weight, specific gravity: 0.91, Mw: 139,034, no acid value)

[0098] <Preparation of polyamic acid solution, a non-thermoplastic polyimide precursor> (Synthesis Example 1) Under a nitrogen atmosphere, 9.0527 g of m-TB (0.04259 mol), 0.9214 g of BAPP (0.00224 mol), and an amount of NMP equal to 15% by weight of solids after polymerization were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 17.6621 g of BP-TME (0.03251 mol) and 2.3641 g of PMDA (0.01084 mol) were added, and the polymerization reaction was carried out by continuing to stir at room temperature for 3 hours to obtain polyamic acid solution 1. The viscosity of polyamic acid solution 1 was 78,582 cps.

[0099] The glass transition temperature of the polyimide film prepared using polyamic acid solution 1 was 246°C, and its storage modulus was 5.5 × 10⁻⁶. 9 Pa (30℃), 6.4 × 10 8 The temperature was Pa (276°C), indicating it was non-thermoplastic.

[0100] (Synthesis Example 2) Under a nitrogen atmosphere, 3.2387 g of m-TB (0.01523 mol), 1.5920 g of TPE-R (0.00544 mol), 0.4470 g of BAPP (0.00109 mol), and an amount of NMP equal to 15% by weight of solids after polymerization were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 8.5745 g of BP-TME (0.01578 mol) and 1.1479 g of PMDA (0.00526 mol) were added, and the polymerization reaction was carried out by continuing to stir at room temperature for 3 hours to obtain polyamic acid solution 2. The viscosity of polyamic acid solution 2 was 40,164 cps.

[0101] The glass transition temperature of the polyimide film prepared using polyamic acid solution 2 was 237°C, and its storage modulus was 4.3 × 10⁻⁶. 9 Pa (30℃), 3.8 × 10 8 The temperature was Pa (267°C), indicating it was non-thermoplastic.

[0102] (Synthesis Example 3) Under a nitrogen atmosphere, 64.20 g of m-TB (0.302 mol), 5.48 g of bisaniline M (0.016 mol), and an amount of NMP that would result in a solid content concentration of 15% by weight after polymerization were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 34.20 g of PMDA (0.157 mol) and 46.13 g of BPDA (0.157 mol) were added, and the polymerization reaction was carried out by continuing to stir at room temperature for 3 hours to obtain polyamic acid solution 3. The viscosity of polyamic acid solution 3 was 28,000 cps.

[0103] The glass transition temperature of the polyimide film prepared using polyamic acid solution 3 was 301°C, and its storage modulus was 9.2 × 10⁻⁶. 9 Pa (30℃), 1.2 × 10 8 It was Pa (331°C) and non-thermoplastic.

[0104] (Combination example 1) 2.25 g of polystyrene elastomer resin (KRATON, trade name: G1652MU) was added to 12.75 g of xylene and completely dissolved. 44.0 g of polyamic acid solution 1, diluted to a solid content of 12% by weight, was added to this solution, and the mixture was stirred using an MS stirrer until a homogeneous solution was obtained, preparing blend solution 1. The composition of blend solution 1 is shown in Table 1.

[0105] (Combination examples 2 and 3) Blend solution 2 or 3 was prepared in the same manner as in formulation example 1, except that polyamic acid solution 2 or 3 was used instead of polyamic acid solution 1, and the polyamic acid / polystyrene elastomer ratio and solvent ratio were changed as shown in Table 1. The compositions of blend solutions 2 and 3 are shown in Table 1.

[0106] (Example 1) Blend solution 1 was uniformly applied to copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rzjis on the resin side: 0.6 μm) so that the thickness after curing would be approximately 32 μm. The solution was then heated and dried at 140°C to remove the solvent. Furthermore, a stepwise heat treatment from 140°C to 320°C was performed for 5 hours to complete the imidization and obtain copper-clad laminate 1.

[0107] Next, the copper foil was etched off the obtained copper-clad laminate 1 using an aqueous ferric chloride solution to prepare a polyimide film 1. Various physical properties were measured for the obtained polyimide film 1. The composition of the polyimide film 1 and the measurement results of various physical properties are shown in Table 2.

[0108] (Example 2, Comparative Example 1) Copper-clad laminates 2 and 3 and polyimide films 2 and 3 were obtained in the same manner as in Example 1, except that the blend solution to be applied and its thickness were changed as shown in Tables 1 and 2. The composition of polyimide films 2 and 3 and the measurement results of various physical properties are shown in Table 2.

[0109] (Comparative Example 2) A polyimide film was prepared in the same manner as in Example 1, except that polyamic acid solution 3 was used instead of blend solution 1. The composition of this polyimide film and the measurement results of various physical properties are shown in Table 2.

[0110] (Comparative Example 3) 2.25 g of polystyrene elastomer resin (KRATON, trade name: G1652MU) was added to 12.75 g of xylene and completely dissolved. The dissolved solution was coated onto a release PET film, heated and dried at 140°C, and the solvent was removed. After solvent removal, the polystyrene elastomer film was peeled off the PET film. Table 1 shows the composition of the resin solution used, and Table 2 shows the composition of the obtained polystyrene elastomer film and the measurement results of various physical properties.

[0111] [Table 1]

[0112] [Table 2]

[0113] Referring to Comparative Examples 1-3, as in Comparative Example 1, by using a predetermined blending ratio of polyamic acid and polystyrene elastomer, the film's CTE can be made to have physical properties close to those of non-thermoplastic polyimide, and its Df can be adjusted according to the blending ratio. However, as in Comparative Examples 1 and 2, if a monomer composition is used that allows for low CTE in the film but results in high Df, low Df and low CTE cannot be achieved simultaneously. In order to achieve low CTE and low Df at a high level, the monomer composition of the polyamic acid must also be devised to allow for low CTE and low Df in the film. As in Examples 1 and 2, by using a polyamic acid containing an acid dianhydride residue represented by general formula (2) and blending it with component (B), it is possible to achieve both low Df and low CTE in the film at a high level. Furthermore, as in Example 2, by adjusting the blending ratio of component (A) and component (B) and the monomer components according to the required CTE range, it is also possible to design a film that prioritizes Df.

[0114] Although embodiments of the present invention have been described in detail above for illustrative purposes, the present invention is not limited to the above embodiments and various modifications are possible.

Claims

1. The following components (A) and (B); (A) Non-thermoplastic polyimide, and (B) Polystyrene elastomer, A polyimide film containing a phase-separated structure, having a thermal expansion coefficient of 50 ppm / K or less, a relative permittivity of 3.0 or less at 10 GHz when measured by a split-post dielectric resonator (SPDR) in an environment of 24-26°C and 45-55% humidity, and a dielectric loss tangent of 0.0030 or less.

2. The polyimide film according to claim 1, having a sea-island structure in which component (A) is the marine phase and component (B) is the island phase.

3. The polyimide film according to claim 1, wherein the content of component (A) is in the range of 50 to 80% by weight and the content of component (B) is in the range of 10 to 50% by weight, relative to the total amount of resin components.

4. The polyimide film according to claim 1, wherein component (A) contains an acid dianhydride residue derived from an acid dianhydride component and a diamine residue derived from a diamine component, and further contains 30 mol% or more of a diamine residue derived from a diamine component represented by the following general formula (1) relative to the total number of diamine residues. 【Chemistry 1】 [In general formula (1), R independently represents an alkyl group having 1 to 3 carbon atoms, which may be substituted with a halogen atom; n represents an integer from 1 to 3; and m represents an integer from 0 to 4.]

5. The polyimide film according to claim 1, wherein component (A) contains 30 mol% or more of acid dianhydride residues derived from an acid dianhydride component represented by the following general formula (2) with respect to the total acid dianhydride residues. 【Chemistry 2】 [In general formula (2), Ar represents a divalent group represented by one of the following:] 【Transformation 3】 [Here, R independently represents an alkyl group having 1 to 3 carbon atoms, which may be substituted with a halogen atom; n1 represents an integer of 1 or 2; and m represents an integer of 0 to 4.]

6. The following components (A1) and (B); (A1) Polyamic acid, and (B) Polystyrene elastomer, It contains the above, and the content of component (A1) is within the range of 50 to 80% by weight and the content of component (B) is within the range of 10 to 50% by weight, (A1) A resin composition containing an acid dianhydride residue derived from an acid dianhydride component and a diamine residue derived from a diamine component, and containing 30 mol% or more of a diamine residue derived from a diamine component represented by the following general formula (1) relative to the total number of diamine residues. 【Chemistry 4】 [In general formula (1), R independently represents an alkyl group having 1 to 3 carbon atoms, which may be substituted with a halogen atom; n represents an integer from 1 to 3; and m represents an integer from 0 to 4.]

7. The resin composition according to claim 6, wherein component (A1) contains 30 mol% or more of an acid dianhydride residue derived from an acid dianhydride component represented by the following general formula (2) with respect to the total acid dianhydride residues. 【Transformation 5】 [In general formula (2), Ar represents a divalent group represented by one of the following:] 【Transformation 6】 [Here, R independently represents an alkyl group having 1 to 3 carbon atoms, which may be substituted with a halogen atom; n1 represents an integer of 1 or 2; and m represents an integer of 0 to 4.]

8. A method for manufacturing a metal-clad laminate comprising an insulating resin layer and a metal layer provided on at least one surface of the insulating resin layer, A method for manufacturing a metal-clad laminate, characterized by comprising the steps of applying the resin composition described in claim 6 or 7 onto the metal layer or onto a base layer provided on the metal layer, and then performing a heat treatment.

9. A metal-clad laminate comprising an insulating resin layer and a metal layer provided on at least one surface of the insulating resin layer, A metal-clad laminate characterized in that the insulating resin layer includes a layer made of a polyimide film as described in any one of claims 1 to 5.

10. A flexible circuit board comprising an insulating resin layer and a wiring layer provided on at least one surface of the insulating resin layer, A flexible circuit board characterized in that the insulating resin layer includes a layer made of a polyimide film as described in any one of claims 1 to 5.

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